Upgrading to FluentValidation 8

FluentValidation 8.0 is a major release that included several breaking changes. Please review this document before upgrading from FluentValidation 7.x to 8.

Asynchronous Validation updates

There have been several major underlying changes to the asynchronous validation workflow in FluentValidation 8. These should not have any impact to any existing asynchronous code other than that some methods now take a CancellationToken when they didn’t before.

These changes were made to remove the internal dependency on the old Microsoft TaskHelper classes and use async/await instead.

SetCollectionValidator is deprecated

Instead of using SetCollectionValidator you should use FluentValidation’s RuleForEach support instead:

FluentValidation 7:

RuleFor(x => x.AddressLines).SetCollectionValidator(new AddressLineValidator());

FluentValidation 8:

RuleForEach(x => x.AddressLines).SetValidator(new AddressLineValidator());

Why was this done?

SetCollectionValidator was added to FluentValidation in its initial versions to provide a way to use a child validator against each element in a collection. RuleForEach was added later and provides a more comprehensive way of validating collections (as you can define in-line rules with RuleForEach too). It doesn’t make sense to provide 2 ways to do the same thing.

Several properties have been removed from PropertyValidator

CustomStateProvider, Severity, ErrorMessageSource and ErrorCodeSource are no longer directly exposed on PropertyValidator, you should now access them via the Options property on PropertyValidator instead.

Why was this done?

It allows extra options/configuration to be added to property validators without introducing breaking changes to the interface going forward.

ValidatorAttribute and AttributedValidatorFactory have been moved to a separate package

Use of the ValidatorAttribute to wire up validators is no longer recommended and have been moved to a separate FluentValidation.ValidatorAttribute package.

  • In ASP.NET Core projects, you should use the service provider to wire models to their validators (this has been the default behaviour for ASP.NET Core projects since FluentValidation 7)
  • For desktop or mobile applications, we recommend using an IoC container to wire up validators, although you can still use the attribute approach by explicitly installing the FluentValidation.ValidatorAttribute package.
  • In legacy ASP.NET projects (MVC 5 and WebApi 2), the ValidatorAttribute is still the default approach, and the FluentValidation.ValidatorAttribute package will be automatically installed for compatibility. However, we recommend using an IoC container instead if you can.

Validating properties by path

You can now validate specific properties using a full path, eg:

validator.Validate(customer, "Address.Line1", "Address.Line2");

Validating a specific ruleset with SetValidator

Previously, if you defined a child validator with SetValidator, then whichever ruleset you invoked on the parent validator will cascade to the child validator. Now you can explicitly define which ruleset will run on the child:

RuleFor(x => x.Address).SetValidator(new AddressValidator(), "myRuleset");

Many old and deprecated methods have been removed

FluentValidation 8 removes many old/deprecated methods that have been marked as obsolete for a long time.

  • Removed the pre-7 way of performing custom validation (Custom and CustomAsync). Use RuleFor(x => x).Custom() instead. See the section on Custom Validators
  • The old localization mechanism that was deprecated with the release of FluentValidation 7. This included several overloads of WithLocalizedName and WithLocalizedMessage. See the section on localization for more details.
  • The RemoveRule, ReplaceRule and ClearRules methods that have been marked obsolete for many years (FluentValidation does not offer a replacement for these as runtime modification of validation rules is not recommended or supported in any way)
  • Removed various async method overloads that didn’t accept a CancellationToken (use the overloads that do accept them instead.)

Other changes

IStringSource.GetString now receives a context, instead of a model. If you have custom IStringSource implementations, you will need to update them.